A car (usually import, more recently domestic) which has no performance modifications to it except a high flow exhaust system that when the driver steps on the gas, makes a sound like you're farting into a bucket.

"Pbbbbbbbbbbbbbbbbbbbbbbbwbwbwbwbwbwbwbwbwbwbbb", said the Honda Civic

"Look at all these high school kids driving around in their fartbuckets."